Problem: 8 rubber stamps cost $8.88. Which equation would help determine the cost of 4 rubber stamps?
There are several equations that could help determine the cost, each with a slightly different approach. Let $x$ represent the unknown cost of 4 rubber stamps. Since 4 rubber stamps cost $x$ , we have the following proportion: $\dfrac{4}{x}$ We can write the fact that 8 rubber stamps cost $8.88 as a proportion: $\dfrac{8}{\$8.88}$ The cost changes along with the number of rubber stamps purchased, and so the two proportions are equivalent. $\dfrac{4}{x} = \dfrac{8}{\$8.88}$